Re: do u ask or do u take
depends- it's a courtesy that drops with time as two people get comfortable around each other. I mean I can't see people that are married for 15 years still asking for permission to take stuff out of a wallet. I think my mom probably used to ask, but if she did now my dad would probably look at her weird if she says 'can I take a 20 out of your wallet?' He'll just say why are you asking- just take it.
I would say, "btw, I took x amount out of your wallet" so they don't get worried someone stole their stuff. It also depends if you are a frivolous spender and finances in the relationship are tight. But I'm pretty responsible w/ money so i would just take it with the "by the way" line. I take $$ from my bro's wallet all the time, and I just tell him I did and he doesn't mind, he does the same with me (although not as often)- we just let each other know so we don't freak out about stolen money. so it depends on the relationship and situation.